How can relative paths in my C# class work with NUnit 3.x?

Question

I have a C# class with the following code.

class Database
{
    private const string DatabaseFilepath = @"Settings\Database.xml";
    ...
    private void LoadDatabase()
    {
        XmlDocument databaseDocument = new XmlDocument();
        databaseDocument.Load(DatabaseFilepath);
    }
}

Now this code executes fine when I compile it, and it is able to read from the Database.xml file. However, when I run a unit test that happens to execute this code using NUnit, I get the following exception.

Result Message: System.IO.DirectoryNotFoundException : Could not find a part of the path 'C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\Settings\Database.xml'.

Now, when I was using Visual Studio Test Tools, this worked perfectly fine. However, upon switching to NUnit, it looks like it is searching in a different working directory. How can I change this?

Note: I have found other questions that ask how to use relative paths in test code. In my example, my relative paths are are in my class code.

Answer 1

Charlie gave a great explanation for why they decided not to change the current directory. For my code under test, I found using AppDomain.CurrentDomain.BaseDirectory and combining it with my relative path using Path.Combine(...) to work fine for NUnit 3.x.